Logitech Webcam c920 - microphone not working, but video working fine - Windows 10

This is a refinement of issue https://answers.microsoft.com/en-us/windows/forum/all/logitech-webcam-c920-microphone-not-working-but/8f47c347-dcf9-4fb0-85d1-6da62ca98198. Recently I discovered my C920 microphone stopped working with all video conference services. I found that test microphone under audio settings saw no input, neither did voice recorder. However, when I went to sound control panel - settings/system/sound/sound control panel (under related settings), then choose the recoding tab and select microphone, then check listen to this device and apply, I got a squeal of feedback - therefore the mic is okay. I followed the advice in the post above but no joy, however through experimentation I found a solution. 

Solution

go to  settings/system/sound/microphone privacy settings (under related settings) and TURN OFF "allow app access for your mic" and Turn off "microphone access for your device" Then go to device manager and uninstall the C920 device under audio input & output. Reboot PC - check mic is seen again in device manager, then turn back on "mic access for device" and turn back on "allow app access for your mic". Mic was then fully functional.

BTW two of my windows 10 PCs had the same problem with C920 and both were fixed by the above process.